In the food industry and the pharmaceutical industry, mixers are widely used for mixing primarily fluid media which may be added one or more solid media. The applied mixers are typically using two different main principles, batch mixing and inline mixing.
A batch mixer consists of a tank in which is provided units for mixing the media in the tank. The medium will circulate in the tank. When the medium in the tank has reached the wanted condition, the tank is to be emptied. In some cases, this occurs by tilting the whole tank and the mixed medium is poured out of the tank from the top and over into a suitable container. In other cases, the tank is provided with a discharge opening at the bottom such that tilting of the tank is avoided. This is particularly advantageous in connection with large tanks. By highly viscous media, emptying of the tank will occur very slowly if only using the action of gravity on the medium. Therefore, it is necessary to arrange special means such that a more rapid emptying of the tank is achieved. The tank top may e.g. be provided with a pressure-tight lid and a compressed air supply in order to force the medium out, but this requires that the compressed air supply is provided with a device for cleaning the compressed air if the mixer is used for foodstuffs, medicine or other media which do not stand up to contamination with uncleaned air. Instead, a pump may be connected to the discharge opening for sucking out the medium. This pump has to be self-priming or be a positive pump disposed below the outlet level of the tank.
Batch mixing will typically take place in connection with mixing of media that are added much dry matter, media that are highly viscous, media that are sticky, and media that are to be mixed for a short time, e.g. emulsions.
An inline mixer also consists of a tank in which there may be provided units for mixing the media in the tank. The bottom of the tank is provided with a discharge opening which normally is shut off. The discharge opening is connected with a pipe between the tank and the shutoff of the discharge opening which discharges into the tank through a filling opening at the upper part of the tank. The medium thus circulates outside the tank. A mixer unit placed in the tank or a pump outside the tank may deliver the required pumping action for maintaining circulation of the medium. The tank is emptied when the medium is sufficiently mixed. This is effected in that the connection between the discharge opening and the filling opening of the tank is shut off simultaneously with the shutoff on the discharge opening of the tank is removed. The mixer unit or the pump outside the tank may be used for quicker emptying of the tank.
Inline mixing will typically find application in connection with mixing of media that are added a little or no dry matter, media with viscosity or media that are to be mixed for a long time.
In connection with certain processes, it is desirable to be able to perform a combination of batch mixing and inline mixing. Such a mixer is known from WO 2006/131800 which discloses a mixer with a mixer unit at the bottom of the tank. Some of the medium circulates within the tank while at the same time another part of the medium is conducted out of a discharge opening and through a pipe which is connected to a filling opening in the tank. This causes a mixing of the medium. The ratio between the part of the medium circulating inside the tank and the part of the medium circulating through the pipe outside the tank is fixed. The ratio is determined on the background of the properties of the media that are desired to be mixed, and the ratio determines the dimension of the mixer. The drawback is that even in the best case and if possible at all, this is associated with a comprehensive rebuilding of the mixer when wanting to process other media. This type of mixer cannot operate exclusively as batch mixer or exclusively as inline mixer, but will only function as a hybrid between the two mixer types.
In various process industries in which mixers are used there is a desire to enable rearranging the process facilities such that different media can be processed. It will additionally be advantageous to perform the switching between batch and inline mixing during the same working process. This will give greater flexibility with regard to the media which can be processed and thereby with regard to which products that may be produced. Also, it will be advantageous to combine the two processing principles in one and the same machine for process industries using both inline and batch mixers, as it becomes possible to lower the capacity costs by minimising the number of mixers.